This invention relates to a method of making an article from a thermoplastic sandwich material, the normals of at least two surfaces of said material mutually forming an angle, said sandwich material comprising a foam core of a thermoplastic foam, and top layers of a thermoplastic synthetic material, which top layers are reinforced with woven fabric, knitted fabric, fibre web or unidirectionally applied fibres.
Sheet-form materials, such as sandwich constructions, are widely used in those areas where materials are used which must combine a great strength or stiffness with a light weight. Examples are applications in aircraft, spacecraft, and transportation, such as maritime and automobile applications.
Sandwich constructions generally consist of a core material which is light in weight, with a mostly reinforced top layer applied to surfaces thereof. By proper bonding between the top layers and the core material the proper stiffness is obtained. The other properties of the material are partly determined by the nature of the various materials.
Known sandwich constructions are based on a core material with a honeycomb structure. Another type of sandwich material is described in European patent applications 264 495 and 269 148. That material is entirely thermoplastic and consists of a core material which contains inter alia a thermoplastic foam and two top layers which consist of a fibre reinforced synthetic material such as polycarbonate or polyetherimide.
European patent application No 88202345.0 discloses a flame-retardant sheet-form material which is also thermoplastic.
In the application of such materials for the construction of articles, such as parts of the interior of aeroplanes, helicopters and the like, it is advantageous when the material can be deformed through the application of heat. European patent application 269,148, mentioned above, discloses a method which makes it possible to obtain two- and three-dimensional deformations of thermoplastic sheet materials consisting of a foam core and reinforced top layers, without any loss of mechanical properties. However, there is also a need for a method of folding such sheet material at an angle, with the mechanical properties being preserved and there being no need of carrying out complex material-removing operations.